Faulty sperm may be the reason women suffer multiple miscarriages, scientists suspect, after finding men whose partners struggle to carry a child to term have more DNA errors.

Researchers at Imperial College in London investigated the sperm quality of 50 men whose partners had suffered three or more consecutive miscarriages.

After comparing the results to the sperm health of 60 male volunteers whose partners had healthy pregnancies, they found the miscarriage group had twice as much damage to their DNA.

Dr Channa Jayasena, lead author of the research from Imperial's Department of Medicine, said: "Traditionally doctors have focused attention on women when looking for the causes of recurrent miscarriage. The men's health - and the health of their sperm - wasn't analysed.

"For instance, previous research suggests sperm has an important role in the formation of the placenta, which is crucial for oxygen and nutrient supply to the foetus."

Recurrent miscarriage is defined as the consecutive loss of three or more pregnancies before 20 weeks' gestation.

The research team believe the DNA damage seen in sperm may be triggered by molecules known as reactive oxygen species, which form in semen and work to protect against bacteria infection.

However, in high concentrations, they can have a harmful effect. The results from the study found sperm from men whose partners had suffered miscarriage had a four-fold increase in the amount of reactive oxygen species compared to the control group.

The research team are now investigating what may trigger high levels of the usually helpful molecules in the hope they could limit their production and save pregnancies.

They suspect they may be over-produced after previous infections.

Dr Jayasena added: "Although none of the men in the trial had any ongoing infection it is possible there may be other bacteria from previous infections lingering in the prostate gland, which makes semen. This may lead to permanently high levels of reactive oxygen species.

"It has taken medicine a long time to realise sperm health has a role to play in miscarriage - and that the cause doesn't lie solely with women.

"Now we realise both partners contribute to recurrent miscarriage we can hopefully get a clearer picture of the problem and start to look for ways of ensuring more pregnancies result in a healthy baby."

The men whose partners had suffered miscarriage were also slightly older than the control group - with an average age of 37 compared to 30, and were slightly more overweight.